The Magnet Field Map
Field on the conductor reaches 16.84 T while the plasma sees 8 T on axis; the full three-dimensional map drives every magnet margin.
One field, many values
There is no single field number for the breeder. The plasma sees 8 T on axis; the inboard conductor sees the 16.84 T peak; and the field varies in magnitude and direction throughout the coil. Because REBCO's critical current depends on both magnitude and angle, the design is checked against the whole field map, not a headline value.
Why the peak is on the inboard leg
In a spherical tokamak the conductor closest to the axis is where the toroidal field is strongest, because field rises toward small major radius. That same location has the least space and the highest neutron flux. The field map therefore concentrates the magnet's worst field, worst force, and worst dose in one region.
- 8 T on axis sets confinement with the 9.66 MA current.
- 16.84 T peak on the inboard conductor sets the structural problem.
- Field angle across the tape sets local critical-current margin.
- Poloidal and screening-current fields add error to the map.
How it is used
The field map is the shared input to stress analysis, critical-current margin, quench modeling, and plasma control. Getting it right is prerequisite to trusting any single margin. It is computed and reproducible, and it is the reference against which magnet feasibility is judged at the FOAK gate.
Poloidal and error contributions
The map is not toroidal field alone: the poloidal-field system and screening-current magnetization add contributions that shift the field the plasma and conductor actually see. Including these in the map is what lets plasma control and magnet margin be judged against reality, which is why the field map is a shared, continuously-updated design reference.
This page documents a design and simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030. Figures are computed, reproducible targets, not measurements.